Right Engine Gear (Circle Survivor)
Spin Gear: Right Engine Gear (Circle Survivor)
Generic Engine Gear with prongs which only fit Circle Survivor.
Generally Rock Bison's Right Engine Gear (Circle Defenser) is more useful due to the additional height it provides, which moves the weight disk out of reach of lower combinations, removing one of the combos main weaknesses.
Still an effective choice however, and may be more useful for lower centre of gravity if not aiming for a compact-on-top Circle Survivor build.
Overall still a competitive part, and quite convenient for Circle Survivor Defense as it comes with Circle Survivor itself.